Add --rotation command-line option

In addition to Ctrl+Left and Ctrl+Right shortcuts, add a command-line
parameter to set the initial rotation.

app/src/scrcpy.c

@@ -396,7 +396,8 @@ scrcpy(const struct scrcpy_options *options) {
                                    options->always_on_top, options->window_x,
                                    options->window_y, options->window_width,
                                    options->window_height,
-                                   options->window_borderless)) {
+                                   options->window_borderless,
+                                   options->rotation)) {
             goto end;
         }